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Open Access Publications from the University of California

Feasible Café Standard Increases Using Emerging Diesel and Hybrid-Electric Technologies for Light-Duty Vehicles in the United States


This paper is concerned with the present status and future projections for emerging technologies that can be utilized in light-duty vehicles in the next five to ten years to significantly reduce their CO2 emissions. The emerging technologies considered are modern clean diesel engines and hybrid-electric powertrains using batteries and/or ultracapacitors for energy storage. Throughout the study, six classes of vehicles –compact passenger cars to large SUVs -were considered. For each vehicle class, computer simulations (Advisor 2002) and cost analyses were performed for conventional ICE and mild and full parallel hybrids using port- fuel injected and lean burn gasoline engines and direct- injection turbo-charged diesel engines to determine the fuel economy and differential costs for the various vehicle designs using the conventional gasoline PFI engine vehicle as the baseline. CO2 emissions (gmCO2/mi) for each driveline and vehicle case were calculated from the fuel economy values. On a percentage or ratio basis, the analyses indicated that the fuel economy gains, CO2 emissions reductions, and cost/price increases due to the use of the advanced engines and hybrid-electric drivelines were essentially independent of vehicle class. This means that a regulation specifying the same fractional reductions in CO2 emissions for all the vehicle classes would not favor one class over the others.

The results of the study were then used to calculate the increase in the CAFÉ standard (miles per gallon gasoline for the new car fleet) that was feasible using each of the emerging technologies and the associated vehicle price increase that would be incurred. It was determined that the CAFÉ standard could be increased to 38 mpg and 48 mpg using the PFI and lean-burn gasoline engines, respectively, in mild hybrids with an associated percentage price increase of 7-9%. The CAFÉ standard could be increased to 42 mpg and 52 mpg using the PFI and lean-burn gasoline engines, respectively, in full hybrids with an associated cost increase of 16-18%. The CAFÉ increases using the diesel engines in mild hybrids were close to those of gasoline engines in full hybrids. The vehicle price increases using diesel engines in hybrids were 17-23% compared to the baseline ICE vehicles using the PFI engine. The fleet CO2 emissions corresponding to the cited CAFÉ standards were 185-234 gmCO2/mi for the mild hybrids using gasoline engines and 170-208 gmCO2/mi for full hybrids. The corresponding values using diesel engines are189-216 gmCO2/mi. The CO2 emissions of the new car fleet for a CAFÉ standard of 27.5 mpg are 322 gmCO2/mi indicating that implementing the hybrid powertrain technologies in the new car fleet could reduce CO2 emissions of the fleet by 25-50%.

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